Prior art systems, both consumer systems and commercial systems, typically employ unbalanced antennas for transmitting and receiving Radio Frequency (RF) signals. Most unbalanced antennas have asymmetrical radiating portions and are fed by unbalanced transmission lines (e.g. coaxial cable or microstrip line) or sources. An example of an unbalanced antenna is a common monopole antenna system that has a single antenna element (a vertical straight metallic post with quarter freespace wavelength long, λ0/4) that is mirrored by a flat horizontal ground plane. There are several reasons why prior art systems employ unbalanced antennas. For instance, much of the commercially available measurement equipment is designed to measure unbalanced antennas. Also, it is often true that for a particular design an unbalanced antenna is smaller in size than its corresponding balanced design. In general, it is more or less halved. For example, a monopole antenna (resonant length λ0/4) is half of the size of a dipole antenna (resonant length λ0/2) for use in the same frequency band. Still further, there are four or five decades of unbalanced antenna engineering and research, such that most designers are more familiar or comfortable with unbalanced systems than with balanced systems.
Many current wireless applications include a low noise amplifier (LNA) or power amplifier (PA) connecting to an antenna element for signal reception or transmission. PAs/LNAs typically have differential, balanced output/input ports. In the signal reception path, in order to connect an unbalanced antenna element to the balanced LNA input, prior art systems include a balun (Balanced Unbalanced transformation) therebetween. In such applications, the balun receives an unbalanced input and transforms it into a balanced output, thereby matching the antenna element to the LNA, but with some amount of loss. In narrow band applications, the loss may be within an acceptable range. However, baluns adapted for use in wide band applications tend to cause loss that may be unacceptable for some devices. Moreover, baluns with wide band characteristic are usually complex and tend to increase design and manufacturing costs. Furthermore, the performance of unbalanced antennas is highly influenced by the geometry of an associated ground plane, especially for ground plane size around 0.25λ0-2λ0, thereby requiring design efforts not only to make a ground plane that can accommodate device circuitry but also to make a ground plane with desirable RF performance.
By contrast, prior art balanced antenna systems tend to be large, and thus, are generally limited to applications wherein minimal loss is more important than space. Further, balanced antenna systems often employ complex impedance matching circuits that are expensive and/or hard to design.